Systemic activation of K-ras rapidly induces gastric hyperplasia and metaplasia in mice.

Mouse models with conditional activation of K-ras (K-ras(G12D)) are used widely to investigate the role of oncogenic K-ras in a tissue-specific manner. However, the effect of ubiquitous activation of K-ras in adult mice has not been well studied. Herein, we report that systemic activation of K-ras in mice leads to rapid changes in gastric cellular homeostasis. Conditional activation of K-ras results in activation of the MAPK pathway and hyperproliferation of squamous epithelium in the forestomach and metaplasia in the glandular stomach. Parietal cells almost completely disappear from the upper part of the stomach adjacent to forestomach of K-ras activated mice. CDX2, a caudal-related homeobox transcription factor normally expressed in the intestine, is upregulated in parts of the stomach, following activation of K-ras in mice. Cyclooxygenase 2 (COX-2), a mediator of inflammation, is also upregulated in parts of the stomach of the K-ras activated mice with concomitant infiltration of hematopoietic cells in the hyperplastic tissue. Moreover, in K-ras activated mice, the expression of putative progenitor cell marker Dcamkl1 is upregulated in the glandular stomach. Expression of CD44, a candidate stomach cancer stem cell marker, is also increased in forestomach and the glandular stomach. These results suggest that cells of the stomach, potentially stem or progenitor cells, are highly susceptible to K-ras activation-induced initiation of gastric precancerous lesions. The histological changes in the K-ras activated mice resemble the pre-neoplastic changes that take place during gastric carcinogenesis in humans. Thus, a mouse model with systemic K-ras(G12D) activation could be useful for studying the early molecular events leading to gastric carcinogenesis.

Production of hydrogen peroxide and redox cycling can explain how sanguinarine and chelerythrine induce rapid apoptosis.

Sanguinarine and chelerythrine are naturally occurring benzophenanthridines with multiple biological activities. Sanguinarine is believed to be a potential anticancer agent but its mechanism of action has not been fully elucidated. We previously found that it causes oxidative DNA damage and very rapid apoptosis that is not mediated by p53-dependent DNA damage signaling. Here we show that sanguinarine and chelerythrine cause the production of large amounts of reactive oxygen species (ROS), in particular hydrogen peroxide, which may deplete cellular antioxidants and provide a signal for rapid execution of apoptosis. Several oxidoreductases contribute to cell death induced by sanguinarine and chelerythrine which appear to be reduced upon entering the cell. We propose a model in which the generation of lethal amounts of hydrogen peroxide is explained by enzyme-catalyzed redox cycling between the reduced and oxidized forms of the phenanthridines and discuss the implications of such a mechanism for potential pharmaceutical applications.

Sanguinarine causes DNA damage and p53-independent cell death in human colon cancer cell lines.

The benzophenanthridine alkaloid sanguinarine has antimicrobial and possibly anticancer properties but it is not clear to what extent these activities involve DNA damage. Thus, we studied its ability to cause DNA single and double strand breaks, as well as increased levels of 8-oxodeoxyguanosine, in human colon cancer cells and found DNA damage consistent with oxidation. Since the tumor suppressor p53 is frequently involved in inducing apoptosis following DNA damage we investigated the effect of sanguinarine in wild type, p53-mutant and p53-null colon cancer cell lines. We found them to be equally sensitive to this plant compound, indicating that cell death is not mediated by p53 in this case. In addition, our observation that apoptosis induced by sanguinarine is initiated very rapidly raised the question whether there is enough time for cellular signaling in response to DNA damage. Moreover, the abundance of double strand breaks is not consistent with only oxidative damage to DNA. We conclude that the majority of DNA double strand breaks in sanguinarine-treated cells are likely the result, rather than the cause, of apoptotic cell death and that apoptosis induced by sanguinarine is independent of p53 and most likely independent of DNA damage.

Two closely related nickel complexes have different effects on DNA damage and cell viability.

Nickel is considered a weak carcinogen. It is known to interact with DNA and DNA-binding proteins. The ability of certain nickel compounds to cleave DNA has been exploited mainly for research purposes and less for developing new anticancer drugs. Here we compare the interactions of two closely related nickel complexes, [NiCR]2+ and [Ni(CR-2H)]2+, with DNA. CR stands for 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene. [NiCR]2+ has been used in the past as a structure-specific probe for RNA and DNA oligonucleotides in the presence of oxidizing agent but little is known about the biological effects of either complex. Our results show that [Ni(CR-2H)]2+ can damage DNA in vivo and in vitro in the absence of an added oxidizing agent and has an IC50 of 70 microM in human breast cancer cells whereas [NiCR]2+ and NiCl2 do not exhibit significant cytotoxicity. However, both [NiCR]2+ and [Ni(CR-2H)]2+ bind to the minor groove of double-stranded DNA.